1. Field of the Invention
This invention relates to a blue light emitting semiconductor device such as a blue light emitting semiconductor laser. This invention also relates to a method of fabricating a blue light emitting semiconductor device.
2. Description of the Prior Art
M. A. Haase et al reported in 1991 that laser diodes were fabricated from wide-band-gap II-VI semiconductors (Appl. Phys. Lett. 59(11), 1272-1274, September 1991). Their laser diodes had a ZnSe-based single-quantum-well structure, and emitted coherent light of a wavelength of 490 nm (blue-green) under pulsed current injection at 77K.
The laser diode of M. A. Haase et al has a laminated structure in which an In electrode layer, an n.sup.+ -GaAs substrate, an n-GaAs buffer layer, an n.sup.+ -ZnSe layer, an n-ZnSSe layer, an n-ZnSe layer, an undoped CdZnSe layer, a p-ZnSe layer, a p-ZnSSe layer, a p.sup.+ -ZnSe layer, a polyimide layer, and an Au electrode layer are arranged in the order. The CdZnSe layer defines a light emitting region (an active layer) providing a quantum well. The CdZnSe layer, that is. the active layer, has a thickness of about 10 nm. The n-ZnSe layer and the p-ZnSe layer are light guiding layers between which the CdZnSe layer (active layer) extends. The p.sup.+ -ZnSe layer forms a cap layer. The polyimide layer has a stripe groove in which the p.sup.+ -ZnSe layer and the Au electrode layer directly contact with each other. The stripe groove in the polyimide layer provides current confinement.
In the laser diode of M. A. Haase et al, the carrier concentration of the p.sup.+ -ZnSe layer (cap layer) is approximately equal to 10.sup.17 cm.sup.-3, and this value of the carrier concentration tends to be inadequate to provide good ohmic contact with the Au electrode layer. Generally, in laser diodes, a small contact resistance at an electrode is desirable since a large contact resistance causes heat and a reduction in carrier injection efficiency.
In the laser diode of M. A. Haase et al, great lattice mismatches tend to occur among the n-ZnSe layer (light guiding layer), the CdZnSe layer (active layer), and the p-ZnSe layer (light guiding layer).